JPH02184569A - Production of silicon carbide molded product - Google Patents

Abstract

PURPOSE:To contrive to improve the characteristics, such as physical properties and heat resistance, of a silicon carbide final molded product and largely shorten a crosslinking non-fusing process by allowing an oxygen-containing organic acid to absorb to or act on an organic silicon polymer molded product and subsequently sintering the product in an inert gas atmosphere. CONSTITUTION:An organic silicon polymer is formed into a shape such as fiber, tape, film or sheet. An oxygen-containing organic acid is allowed to adsorb to and/or act on the formed product in an amount of 0.01-300wt.% based on the weight of the formed product. The product is treated with a basic substance, if necessary, preliminarily calcined and subsequently sintered in an inert gas atmosphere to provide the objective product. The organic silicon polymer as a raw material is especially preferably a polycarbosilastyrene copolymer. The oxygen-containing organic acid includes methane sulfonic acid, trichloroacetic acid, formic acid and oxalic acid. The basic substance is most preferably ammonia.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is a silicon carbide-based molded product (m-fiber 9) that uses an organosilicon polymer as a raw material and has good physical properties and heat resistance.
This invention relates to a method for efficiently manufacturing tapes, films, sheets, thin sheets, etc.).

[Prior Art] Conventionally, polysilastyrene as described in U.S. Pat. It is known to manufacture silicon carbide molded products by molding into fibers, etc., making them invulnerable by cross-linking by irradiating them with ultraviolet rays, electron beams, etc., and then firing them (Japanese Patent Laid-Open No. 58-21542).
No. 6) However, this method is not suitable for industrial implementation because of the shrinkage and fusion of the molded product (for example, fibers) during crosslinking and infusibility.

For this reason, the present inventors first added polysilastyrene to a polycarbosilastyrene copolymer by heat-treating and/or ultraviolet irradiation treatment, and then molding it by a melting method or a dry method, By heat-treating the obtained molded product in air to make it invulnerable, and then firing it in an inert gas, we can produce high-quality silicon carbide molded products much more efficiently than conventionally known methods. how to(
(See U.S. Pat. No. 4,743,411). However, even with this method, a large amount of oxygen is incorporated into the polymer during the crosslinking and infusibility stage, so the physical properties of the silicon carbide molded product ultimately obtained are not necessarily sufficient, and polycarbosilastyrene copolymer moldings There remains the problem that it takes a considerable amount of time to process things to make them invulnerable.

There is also a known method for producing silicon carbide molded products using polycarbosilane as a precursor polymer (
Special Publication No. 57-53892, No. 58-38534.

No. 60-28927, etc.), as in the case described above, the amount of oxygen taken into the polymer during the crosslinking and infusibility stage is large, and the physical properties of the silicon carbide molded product obtained are not sufficient. There is a problem that it takes a long time.

Furthermore, a method of manufacturing silicon carbide molded products using polycarbosilanes containing a small amount of other metal elements such as polycarbotitanosiloxane as a precursor polymer is also known (for example, Japanese Patent Publication No. 1405/1983). However, this method also has the same problems as described above.

[Object of the Invention] The first object of the present invention is to improve the physical properties such as strength and modulus, and heat resistance of the final molded product in a method for producing silicon carbide molded products from organosilicon polymers. The second objective is to improve productivity by significantly shortening the crosslinking process for making organosilicon polymer molded articles invulnerable.

[Structure of the Invention] The object of the present invention as described above is to form an organosilicon polymer into a fiber, tape, film, sheet, 'l1 leaf, etc.
An oxygen-containing organic acid is adsorbed and/or acted on the organosilicon polymer molded article in an amount of 0.01 to 300% (by weight) based on the molded article, then a basic substance is applied thereto, and if necessary, after pre-calcination, This is achieved by the method of the invention, characterized in that the organosilicon polymer is converted into silicon carbide by calcination in an inert gas atmosphere.

Each component of the method of the present invention will be explained in detail below.

In the method of the present invention, the organosilicon polymer used as a raw material is an organosilicon polymer that is a precursor of silicon carbide, such as polysilastyrenes, polycarbosilanes, polycarbosilastyrene copolymers, etc. used. It may also be a co-decomposed polymer of these two types, and among these, polycarbosilastyrene copolymer is particularly preferred.

As a method for synthesizing such polymers, for polysilastyrenes, for example, dichlorodimethylsilane and dichloromethylphenylsilane are reacted in an inert solvent such as toluene or xylene using a sodium metal catalyst at a temperature above their melting point. Can be adopted.

The composition of such polysilastyrenes is represented by the following formula, CHs
C@H (in the above formula, R is CH, or cs H5, n is 10-30
In the polymer compound represented by (an integer of 00), those in which the value of X is in the range of 0.2 to 0.9, preferably in the range of 0.3 to 0.7 are used.

In addition, a small amount of polysilanes may be used together with the above-mentioned polysilastyrenes.

Such a method for producing polysilastyrene is described in detail in, for example, US Pat. No. 4,324,901 and Japanese Patent Publication No. 82-96)2.

Further, the polycarbosilane used in the method of the present invention can be synthesized, for example, by thermal decomposition transition reaction of polydimethylsilane. An example of such a method is West German Patent Publication No. 2,236,078, U.S. Pat. No. 4,052,43.
No. 0, Japanese Patent Publication No. 57-26527, etc.

On the other hand, the polycarbosilastyrene copolymer preferably used in the method of the present invention is disclosed in U.S. Pat.
As described in the issue, it is a special organosilicon polymer,
The coelectric body is produced by converting the above-mentioned polysilastyrenes into a polycarbosilastyrene copolymer by subjecting them to a heat treatment and/or an ultraviolet irradiation treatment.

The heat treatment of polysilastyrenes is carried out in a temperature range of 300 to 500°C, preferably in a temperature range of 350 to 450°C. The heat treatment time is appropriately selected within the range of 5 minutes to 10 hours depending on the heat treatment temperature.

That is, the heat treatment temperature and time are approximately 3
~10 minutes; at 450°C, approximately 10 to 100 minutes is sufficient.

In addition, in the treatment by ultraviolet irradiation, for example, the output 5
20-20 using ~500W/csn UV lamp
Preferably, the irradiation is carried out at a temperature of 0°C.

When polysilastyrenes are heat-treated or UV irradiated according to the above method, some benzene is produced as a low-boiling substance, and at the same time, carbosilane (Si) is produced by rearrangement of methyl groups.
As CH2) bonds are generated, the molecular weight is increased due to partial crosslinking, the softening point increases, and the molding temperature also increases.

The polycarbosilastyrene copolymer referred to in the present invention is a general term for organosilicon polymers having carbosilane bonds, silastyrene bonds, and partially crosslinked bonds. It is preferable that the copolymerization molar ratio of carbosilane bonds and silastyrene bonds is 3 to 7:3.

These various organosilicon polymers may contain small amounts of bonds such as -Ti-0+, -Zr-0-, etc. as required. Methods for introducing such bonds include, for example, Japanese Patent Publication No. 1405/1983. As described in , a mixture of polycarbosilane and polytitanosiloxane is heated in an organic solvent under an inert atmosphere to convert at least a portion of the silicon atoms of the polycarbosilane and the silicon atoms of the polytitanosiloxane. /or by bonding at least a portion of titanium atoms via oxygen atoms.

In the method of the present invention, the organosilicon polymer used for molding may contain a small amount (for example, 20% by weight or less of the organosilicon polymer in the case of fibers) of an organic lubricant, a modifier, a crosslinking agent, a stabilizer, etc. may contain additives.

Organic lubricants are higher fatty acids and higher fatty acid esters.

Higher fatty acid amides, higher alcohols, etc. are used singly or in a mixture, and examples of these compounds include, but are not limited to, the following substances. Namely, as higher fatty acids, caprin, acid,
Lauric acid, palmitic acid, margaric acid, stearic acid, oleic acid, etc. Higher fatty acid esters include capric acid ester, nonyl acetate, lauric acid ester.

Esters of the above-mentioned higher fatty acids such as ethyl stearate, butyl stearate, etc.; Higher fatty acid amides include oleic acid amide, linoleic acid amide, linoleic acid amide, stearic acid amide, etc.; higher alcohols include caprylic alcohol, decyl alcohol, and lauryl. Examples include alcohol, oleyl alcohol, and stearyl alcohol. These are particularly useful when manufacturing sheet-like molded products.

Furthermore, a small amount of Si fine powder, TiR powder, SIC fine powder, Tic fine powder, etc. may be added within a range that does not impair moldability.

Organosilicon polymer fibers and tapes as described above.

Molding methods for films, sheets, thin sheets, etc. include melting method,
Either dry method (solution method) may be used; in the case of melt method,
The organic silicon polymer is discharged into a cooled atmosphere and cooled to solidify. In the dry method, a dope in which the organic silicon polymer is dissolved in an organic solvent is extruded through a nozzle or slit, and the solvent in the dope is removed by evaporation. A method of coagulating is adopted. Industrially, a melting method is preferable, and this melting method is described in US Pat. No. 4.7 proposed by the present inventors.
It is described in detail in No. 43,411.

In this way, after forming a molded product such as a #1 cloth, the molded product is rendered invulnerable and converted into a silicon carbide-based molded product by firing. In conventional technology, infusibility is achieved by thermal oxidation by heating in air, but the oxygen contained in the molded product has a negative effect on the physical properties and heat resistance properties of the obtained product, and this oxygen uptake has a large effect. The portion results from infusibility carried out in air or an oxidizing atmosphere. Therefore, it is expected that the physical properties and i1 thermal properties of the silicon carbide molded product will be improved by suppressing the uptake of oxygen as much as possible to make it infusible. However, no method has been found to complete infusibility without the action of oxygen, except for a special example of using radiation (see "Kobunshi" Vol. 37, June issue, p. 466), and it is industrially feasible. It is not yet known that non-oxygen infusibility can be achieved by such a method.

In order to meet these demands, the present inventors previously proposed a low-oxygen infusibility method using halogens (Japanese Patent Application No. 1983).
3-39682), according to this method, the amount of oxygen taken in during infusibility can be dramatically reduced compared to the conventional air infusibility method. However, even in such a low-oxygen infusibility method, it was necessary to incorporate a small amount of oxygen in order to suppress variations in the degree of flame resistance caused by the type of polymer, etc. In view of this situation, the present inventors further As a result of further research to find a method that can achieve infusibility in low oxygen conditions, we found that by sequentially performing treatment with an oxygen-containing m-acid and treatment with a basic substance, it was possible to substantially eliminate oxygen in the atmosphere. The present invention was achieved by discovering that infusibility can be efficiently achieved without the presence of silane.

In the method of the present invention, a molded product such as m-fiber made of an organosilicon polymer is heated with methanesulfonic acid,
Oxygen-containing organic acids such as trichloroacetic acid, formic acid, oxalic acid or acetic anhydride are adsorbed/acted on, and then ammonia,
By reacting a basic substance such as methylamine, ethylenediamine, or 1-limu hydroxide in a non-oxidizing gas, infusibility can be completed in the substantial absence of oxygen. Therefore, it becomes possible to suppress the oxygen content of the silicon carbide molded product obtained by firing to a low level, and the properties such as physical properties and heat resistance of the molded product are improved.

Examples of the oxygen-containing organic acids used in the method of the present invention include halogen-substituted acetic acids such as trichloroacetic acid vi1 dichloroacetic acid, monochloroacetic acid, and formic acid.

Examples include compounds having a carboxyl group such as oxalic acid, such anhydrides such as acetic anhydride, and compounds having a sulfuric acid group such as methanesulfonic acid and para-toluenesulfonic acid.

The amount of oxygen-containing organic acid to be adsorbed/acted is 0.01 to 3 CO based on the weight of the molded product (for example, fibers immediately after spinning).
(heavy fL)%, especially from 0.1 to 1
00% (by weight) is preferred.

Adsorption/action methods include a method of placing an organosilicon polymer molded article (for example, a fiber after spinning rfL) in the vapor of the above acid, and a method of placing an organosilicon polymer molded article in a solution (for example, an aqueous solution, etc.) in which the above acid is dissolved. Any method can be employed, such as a method of immersing the organic silicon polymer molded product, a method of applying a treatment agent containing the above acid to the organosilicon polymer molded product, and the like.

The atmosphere in which the oxygen-containing organic acid is adsorbed/acted on is preferably an inert gas atmosphere or a vacuum atmosphere.

This can be understood to be because, in such an atmosphere, the action of oxygen accompanying the adsorption/action of acid is reduced.

The organosilicon polymer molded article on which the oxygen-containing m-acid has been adsorbed and acted upon in this manner is then subjected to the action of a basic substance in a non-oxidizing atmosphere.

Examples of the basic substance used in the present invention include ammonia, sodium hydroxide, and potassium hexahydroxide.

Examples include methylamine and ethylenediamine, among which ammonia is most preferred.

A non-oxidizing atmosphere is preferable as the atmosphere in which the basic substance is applied.The method for realizing such an atmosphere differs depending on whether the basic substance used is supplied in gaseous or liquid form. That is, when supplied in gaseous form,
Only the gas of the basic substance, or the gas of the basic substance and nitrogen.

A mixture of inert gases such as hydrogen, argon and helium is used. On the other hand, if the basic substance is supplied in liquid form, an aqueous solution of the basic substance is usually used, but in such a case, it is preferable to remove the excess basic substance by washing with water, etc. In order to prevent the incorporation of oxygen, it is preferable to operate under an inert gas atmosphere or at low temperatures.

The amount of the basic substance to be applied varies depending on the amount of the organic acid that has been adsorbed/acted on in advance, but it is preferable that the basic substance be applied in sufficient excess to the aerobic acid. A range of equivalents to 400 equivalents is preferably adopted.

In the method of the present invention, there is no particular restriction on the temperature at which the basic substance is applied.
Alternatively, the action of the organic silicon polymer and the basic substance starts extremely quickly. However, from the viewpoint of operability, the temperature is generally from room temperature to 200°C.

In this way, the melting point of the organosilicon polymer molded product treated with an oxygen-containing organic acid and then with a basic substance is significantly higher than that of the original (before treatment) polymer, and the molded product is Temperature at which high-order polymerization/crosslinking begins and the melting point begins to rise rapidly, e.g. 350°C to 400°C
It does not melt even at temperatures of That is, the shape of the molded product is maintained and the molded product is in a state where it can be converted into an inorganic substance without being fused to each other, thus achieving the purpose of infusibility. Additionally, according to experiments conducted by the present inventors, organosilicon polymers treated according to the present invention remain insolubilized in good solvents for the original polymer, such as toluene, even if the treatment with basic substances is carried out at room temperature. Therefore, it is considered that cross-linking has already been formed in the method of the present invention.

For these reasons, organosilicon polymer moldings that have been adsorbed/acted with oxygen-containing organic acids and then acted upon with basic substances can omit the cross-linking and infusibility process using oxygen and heat, which was previously essential, and can be used as is. By subjecting it to high-temperature firing, it can be made into silicon carbide-based molded products.

However, this must first be carried out using an inert gas (
After preliminary firing (heat treatment) for 1 minute to 3 hours in an inert gas (nitrogen, etc.) at 800 to 1400°C.

It is also possible to make desired silicon carbide-based molded products (fibers, etc.) by baking in argon, etc.) for 1 minute to 2 hours.

<Effects of the Invention> Since the silicon carbide molded product thus obtained contains only a small amount of oxygen, its heat resistance properties and mechanical properties in air are significantly improved.

Further, according to the method of the present invention, the infusibility treatment for firing the organosilicon polymer molded article can be simplified, and the pre-baking time in an inert gas can also be shortened. Physical properties such as strength and modulus of the resulting molded product are improved,
Moreover, variations in physical properties within the same lot are also reduced.

Also, compared to the previously proposed method using halogen,
It is advantageous in terms of ease of handling before treatment, corrosion of equipment, etc.

Therefore, the method of the present invention is extremely useful as a method for industrially producing high quality silicon carbide fibers, tapes, films, etc.

<Examples> Next, Examples and Comparative Examples of the present invention will be described in more detail, but the present invention is not limited thereto.

Example 1 Polysilastyrene (softening point 86-94°C) obtained by polymerizing equimolar amounts of dichlorodimethylsilane and dichloromethylphenylsilane at 110°C using a sodium dispersed catalyst in a toluene solvent was used. Heat-treated at 400°C for 30 minutes in an inert gas (nitrogen), and then treated at the same temperature under reduced pressure for 5 minutes to obtain a polycarbosilastyrene copolymer with a softening point of 230-240°C and an average molecular weight of was 4,600, and the ratio of carbosilane bonds to silastyrene bonds was 45,155.

A polycarbosilastyrene copolymer fiber obtained by melt-spinning this copolymer at 280° C. and 600 m/min is placed in a pressure container with 10% trichloroacetic acid based on the weight of the raw fiber,
After repeating the operation of drawing a vacuum to 0.2 Torr and breaking it with high-purity nitrogen to completely replace the internal oxygen, create a nitrogen atmosphere and apply trichloroacetic acid to polycarbosilastyrene copolymer fibers at 180°C for 1 hour. adsorbed/acted on. Thereafter, the inside of the container was completely purged with nitrogen, then replaced with ammonia gas, and allowed to react at 180° C. for 1 hour. After that, the treated fibers were taken out and 10g/10
The fibers were fired in nitrogen at 1200° C. under a load of 000 de, and converted into silicon carbide fibers. The silicon carbide fiber thus obtained had a thread diameter of 5.2 μm and a strength of 330 kg/−. Further, after exposing the silicon carbide fiber to air at 1200° C. for 1 hour, the strength retention rate was measured, and as a result, no deterioration was observed.

Example 2 A polycarbosilastyrene copolymer synthesized by a method similar to that shown in Example 1 was heated at 280°C for 600 m
The obtained polycarbosilastyrene copolymer fiber was melt-spun at a speed of 100% per minute, and the resulting polycarbosilastyrene copolymer fiber was placed in a pressure vessel with 20% @acid based on the weight of the raw yarn, evacuated to 0.2 Torr, and then heated with high-purity nitrogen. After repeating the breaking operation to completely replace the internal oxygen, a nitrogen atmosphere was created and the acid was adsorbed onto the polycarbosilastyrene copolymer fibers at 180°C for 1 hour.
It worked. Thereafter, the inside of the container was completely replaced with nitrogen, and then replaced with ammonia gas, and left to react at room temperature for 1 hour. After that, take out the treated fibers and
The fibers were fired in nitrogen at 12 GO C under a load of g/1ooooode to convert them into silicon carbide fibers. The silicon carbide fiber thus obtained had a thread diameter of 5.2 μm and a strength of 320 kg/-. Furthermore, after exposing the silicon carbide fibers to air at 1200° C. for 1 hour, the strength retention rate was measured, and as a result, the fibers showed no deterioration at all.

Example 3 A polycarbosilastyrene copolymer synthesized by a method similar to that shown in Example 1 was heated at 280°C for 600 m
The resulting polycarbosilastyrene copolymer fibers were placed in a pressure vessel together with 10% oxalic acid based on the weight of the raw fibers, evacuated to 0°2 TOrr, and then heated with high-purity nitrogen. Repeat the breaking operation to completely replace the oxygen inside, create a nitrogen atmosphere, and heat at 180℃ for 1 hour.
Oxalic acid was allowed to adsorb/act on polycarbosilastyrene copolymer fibers for a period of time. After that, the inside of the container was completely replaced with nitrogen, then replaced with ammonia gas, and left at room temperature for 1 hour.
I let time work. After that, take out the treated fiber 10
It was fired in nitrogen at 1200° C. under a load of 0 t/10000 de to convert it into silicon carbide fiber. The strength of the silicon carbide fiber thus obtained is 336)
It showed qr/-. In addition, the silicon carbide fiber is
After being exposed to air at 200° C. for 1 hour, strength retention was measured and the fibers showed no deterioration at all.

Example 4 Dichlorodimethylsilane was polymerized at 110 to 120°C using a sodium dispersed catalyst in a xylene solvent to obtain a white powdery polysilane. The mixture was heat-treated for a period of time, and then treated at 300° C. under reduced pressure to remove low-boiling substances to obtain polycarbosilane. After this raw material polymer was once dissolved in a toluene solvent, toluene-insoluble matter was removed by r-filtration, and toluene was further removed from the filtrate under reduced pressure to obtain a polymer free of foreign matter. This purified polymer was heated at 280℃ for 3
The fibers were melt-spun at 00 m/min to obtain polycarbosilane fibers. This fiber was placed in a pressure container with 30% methanesulfonic acid based on the original fiber, and the vacuum was drawn to 0.2 Torr.The operation of breaking the fiber with high-purity nitrogen was repeated, and after completely replacing the oxygen inside, nitrogen Atmosphere: 180℃
Methanesulfonic acid was allowed to adsorb/act on the polycarbosilastyrene copolymer fibers for 1 hour. After that, the inside of the container is completely replaced with nitrogen, and then replaced with ammonia gas,
The mixture was allowed to act as it was at room temperature for 1 hour.

Subsequently, the inside of the container was replaced with nitrogen to create an inert atmosphere, and then the temperature was raised from room temperature to 350° C. and kept at that temperature for 2 hours to perform preliminary firing. Thereafter, the treated fibers were taken out and fired at 1200° C. in nitrogen under a load of 100 t/10000 de to convert them into silicon carbide fibers. The silicon carbide fiber thus obtained had a thread diameter of 7.0 μm and a strength of 310 kg/−. Moreover, when the strength of the silicon carbide fiber was measured after being exposed to air at 1200° C. for 1 hour, no deterioration was observed.

Comparative Example 1 A polycarbosilastyrene copolymer synthesized by the same method as that shown in Example 1 was melt-spun at 280° C. and 600 m/min to obtain a polycarbosilastyrene copolymer fiber. The fibers were heat-treated in air at 120°C for 3 hours, and then subsequently heat-treated in air at 180°C for 3 hours. Thereafter, the fibers were pre-calcined under a load of 100g/1"0O00de at 350°C for 2 hours in a container with a nitrogen stream passed through them. Thereafter, the treated fibers were subjected to 100 g
The fibers were fired at 1200° C. in nitrogen under a pressure of 10,000 de R and converted into silicon carbide fibers. The silicon carbide fiber thus obtained had a thread diameter of 8.8 μm and a strength of 200 kg/−. Further, when the strength of the silicon carbide fiber was measured after being exposed to air at 1200° C. for 1 hour, the strength retention rate was 40%.

Claims (7)

[Claims] (1) Organosilicon polymer can be used as fiber, tape, film, etc.
After molding into a sheet, thin film, etc., the organosilicon polymer molded product is adsorbed and/or acted upon with an oxygen-containing organic acid in an amount of 0.01 to 300% (by weight) based on the weight of the molded product, and then a basic 1. A method for producing a silicon carbide molded article, which comprises applying a substance, pre-calcining if necessary, and then firing in an inert gas atmosphere. (2) The production method according to claim (1), wherein the organosilicon polymer is a polycarbosilastyrene copolymer formed by heat treating and/or ultraviolet irradiation treatment of polysilastyrenes. (3) The production method according to claim (1) or (2), wherein the oxygen-containing organic acid is at least one selected from the group consisting of methanesulfonic acid, trichloroacetic acid, formic acid, oxalic acid, and acetic anhydride. . (4) Claims (1) to (4) wherein the oxygen-containing organic acid is adsorbed and/or acted on the organosilicon polymer molded article in an inert atmosphere.
The manufacturing method according to any one of 3). (5) Claims (1) to 1, wherein the basic substance is ammonia.
The manufacturing method according to any one of (4). (6) The production method according to any one of claims (1) to (5), wherein the organosilicon polymer molded article adsorbed/or acted upon with an oxygen-containing organic acid is acted upon with a basic substance in a non-oxidizing atmosphere. (7) After adsorbing and/or acting on the organosilicon polymer molded article with an oxygen-containing organic acid, and then allowing a basic substance to act on it,
The production according to any one of claims (1) to (6), wherein pre-calcination is performed in an inert gas at a temperature of 200 to 800°C, followed by firing in an inert gas at a temperature of 800 to 1400°C. Law.